The present invention relates to a sensor for measuring a magnetic field which comprises several electrically semiconductive layers.
Sensors for measuring a magnetic field are used in many fields today. They are, for example, used in automation, control and measuring technology in order to measure distances in a contact-free manner, to ascertain speeds or to test positionings. In information technology, miniaturized magnetic field sensors read digital data which are, for example, magnetically stored on hard drives. Sensitive magnetic field sensors are used in non-destructive material testing in order to detect material defects. In medical diagnostics, highly sensitive sensors are used to quantitatively record biomagnetism.
The sensors must meet quite a few different requirements corresponding to the diversity of applications. This can be accomplished with sensors which consist of different materials (such as metals, semiconductors or superconductors and which are based on different physical principles.
The individual sensors can thereby be roughly divided into the following types:
field plates, Hall probes, magnetic diodes and magnetic transistors consisting of semiconductors;
magnetic resistive homogeneous or granular layers and layer systems consisting of metals and insulators;
SQUIDS consisting of superconductors
The types of sensors used most often are:
[1] field plates consisting of InSb with NiSb needles,
[2] Hall probes made of silicon or III/V semiconductors,
[3] magnetic resistive AMR sensors which consist of a homogeneous thin magnetic metal layer of, for example, NiFe,
[4] GMR sensors which consist of at least two magnetic metal layers and a non-magnetic metal layer and
[5] SQUIDS consisting of the superconductors Nb or YBCO whose operating temperature is at 4K or 80K, respectively.
The sensitivity of the sensors vis-à-vis a magnetic field or a change in the magnetic field increases continuously from the top to the bottom in the above arrangements.
The following is noted briefly about the mode of operation of the individual types of sensors:
The reason for the change in resistance in the field plates [1] and for the Hall voltage [2] is the Lorentz force which is produced at electrical charges when they move in the magnetic field.
In AMR sensors [3], the change in resistance is based on a magnetic scattering of the conduction electrons which changes with the direction of the magnetizing relative to the direction of the current.
In the GMR [4], the action is again based on an anisotropic scattering at the contact surfaces which depends on the angle that both magnetizations form with one another.
In the SQUIDS [5], the magnetic behaviour is determined by the principle that the magnetic flow in a superconductive ring must be an integral multiple of the elementary flow quantum.
The object of the present invention is to create a sensor for measuring a magnetic field which is very sensitive and, as a result, can already be used to measure the smallest magnetic fields or to measure the changes in magnetic fields. Moreover, it should be able to operate at room temperature and not exhibit any hysteresis manifestations.
This object is solved with the sensor of the invention according to claim 1 which consists of several electrically semiconductive layers which are arranged in the form of a diode or pin diode connected in reverse direction. This layer arrangement comprises an anode layer, a cathode layer and an intrinsically conductive layer enclosed between the two. The anode layer is subdivided by insulation sections, for example in the form of insulating strips, into several anode layer areas that are insulated from one another. The cathode layer has an injector area on the areas opposite the insulation sections which is oppositely doped. The anode layer and the cathode layer are connected with an inverse voltage, so that the layer arrangement is biased in reverse direction. An injection voltage is applied to the injector area in the cathode layer. As a result, an electron beam is formed between the injector area and the anode thereby that injected electrons move from the injector area on the cathode to the anode lying opposite thereto. A distribution of the electron beam takes place thereby due to thermal diffusion. This distributed electron beam now uniformly strikes the individual anode layer areas insulated from one another. The anode layer areas are individually earthed by respective current measuring devices. Thus, depending on the number of anode layer areas, a corresponding part of the entire electron beam will strike every single anode layer area. This part of the electron beam can be measured in the form of a current with the respective current measuring device.
If a magnetic field is now applied in the intrinsically conductive layer diagonally to the direction of dispersion of the electron beam which extends between injector area and anode layer, the Lorentz force is then exerted on the drifting electrons which results in a diversion of the electron beam. This diversion of the electron beam leads thereto that other partial amounts of the entire electron beam now strike the individual anode layer areas insulated from one another, which results in a corresponding change of the partial current of the anode layer areas. The magnetic field can be calculated from this change of the partial currents.